a) Field of the Invention
The invention is directed to a linear motion leadthrough for a rod having a first end, a second end and an outer surface, its first end projects into a vacuum area of a vacuum installation and its second end is located outside of the vacuum area, wherein the linear motion leadthrough comprises:
a bushing which has an inner wall and through which the rod extends and is displaceable linearly relative to the rod,
at least one elastomer sealing ring for sealing the rod relative to the bushing which is secured to the inner wall of the bushing or to the outer surface of the rod, wherein the sealing ring is lubricated by a lubricant.
b) Description of the Related Art
Bellows leadthroughs and linear motion leadthroughs are known for purposes of guiding a rod into the vacuum area of a vacuum installation, wherein the rod is to be mounted so as to be displaceable linearly. Bellows leadthroughs, which can be constructed as expansion bellows or corrugated bellows, have the advantage that they are completely vacuum-tight and free from grease, that is, no lubricant is required. The disadvantage of bellows leadthroughs is their high price. These bellows are also critical with respect to application because a strong, rapid intrusion of air into the vacuum can come about in case of failure of the bellows.
In linear motion leadthroughs, the outer surface of the rod is sealed relative to the inner surface of the bushing through which the rod passes into the vacuum area by means of one or more elastomer sealing rings. For example, one or more O-rings which contact the outer surface of the rod can be arranged at the inner wall of the bushing. When the rod is displaced, these O-rings slide along the outer surface of the rod. Other sealing rings such as lip seals are also known.
These linear motion leadthroughs are inexpensive to produce. It is also advantageous that leakage, if it occurs, generally does so at a slow pace so that there will not be any sudden strong influx of air into the vacuum. However, lubrication with lubricant is required for linear motion leadthroughs of this type. Due to repeated displacement of the rod, this lubricant is also pushed in direction of the vacuum-side end of the rod, where lubricant can accumulate over time.
The lubricant can easily spread to other parts in the vacuum area of the vacuum installation. For example, the interiors of vacuum installations are occasionally cleaned by venting and opening the vacuum installation and wiping down the inner walls with cloths. In so doing, the cloth can easily contact accumulated lubricant at the rod so that the lubricant is spread. It has also been observed that accumulations of lubricant often detach by themselves and the lubricant is deposited on other parts of the chamber in a troublesome manner.
Linear motion leadthroughs in which a cover ring is arranged before the final sealing ring on the vacuum side and the rod passes through the cover ring with slight clearance are also already known. A cover ring of this kind can provide a certain degree of protection against unwanted and disadvantageous penetration of particles into this sealing ring. However, it has been observed that a cover of this kind can not permanently hold back the lubricant for the sealing rings, so that accumulations of lubricant can nevertheless develop over the course of time on the portion of the rod projecting into the vacuum.
An important object of the invention is to provide a linear motion leadthrough in which the spread of lubricant to other parts in the vacuum area is substantially reduced.
A linear motion leadthrough according to the invention for a rod which has a first end, a second end and an outer surface and whose first end projects into a vacuum area of a vacuum installation while its second end is located outside of the vacuum area, comprises:
a bushing which has an inner wall and through which the rod extends and which is displaceable linearly relative to the rod,
at least one elastomer sealing ring for sealing the rod relative to the bushing which is secured to the inner wall of the bushing or to the outer surface of the rod, wherein the sealing ring is lubricated by a lubricant, and
a bellows which is arranged inside the vacuum area, has a first end and a second end, encloses a portion of the rod located inside the vacuum area and delimits a space located between the rod and the bellows from a space lying outside the bellows, and whose first end is fastened to the rod and whose second end is fastened to the bushing or to a part enclosing the bushing, wherein at least one opening is provided which connects the space between the rod and the bellows with the space outside the bellows.
Accordingly, in the linear motion leadthrough according to the invention the bellows is not a sealing element for sealing against air or gas and the space enclosed by the bellows forms a part of the vacuum area of the vacuum installation. The at least one opening connecting the space between the rod and the bellows with the space outside the bellows is provided for purposes of pumping out the space enclosed by the bellows. For this purpose, one of more openings can be formed in the bellows itself. It is also conceivable and possible in principle, for example, to provide one or more bore holes in the rod which connect the space outside the bellow with the space enclosed by the bellows.
These one or more openings can be formed so as to be very small with respect to surface in relation to the entire surface of the bellows, so that, in practice, lubricant detaching from the rod does not exit from the opening or openings or, if so, only to an insignificant extent. Further, the bellows forms a protection against contact for the part of the rod enclosed by the bellows so as to prevent spreading of lubricant due to contact with the rod.
In an advantageous embodiment example of the invention, the bellows diaphragm at the first end of the bellows reaches further inward than the other bellows diaphragms, wherein radial notches proceed from the inner edge of this bellows diaphragm so as to form openings in the bellows. A plurality of such notches are provided in circumferential direction, wherein a snap-in tongue which can snap into a snap recess in the rod is delimited by every two notches. The notches provided in this embodiment example accordingly have a dual function: on the one hand, they form openings in the bellows, on the other hand, snap-in tongues are formed for fastening the first end of the bellows to the rod.
The different features and constructions according to the invention are set forth in the claims.
Further advantages and details of the invention are described in the following with reference to the embodiment example shown in the drawings and additional objects of the invention follow therefrom.